Because they’re there. Because you don’t want to leave a great gun lying on the street to be run over and destroyed, in case you ever need it. And to grab the ammo and magazines out of, of course, and a handy source of mods.
I’ve definitely had multiple hauling spaces, plus the floor tiles underneath, filled with just guns (no ammo, no magazines, no mods or accessories). And that’s with leaving behind most of what I find, taking only the good stuff.
After all, collecting guns is much easier if your gun safe is travelling with you.
That’s my point, you won’t ever need a replacement because guns do not degrade. Even fouling is just a nuisance, not a problem. Yeah, it takes 50 minutes to clean it… after like several thousands of rounds spent. Whatever, I can live with it.
Losing, misplacing, accidentally dropping it, forgetting where you put it down, accidentally running over it, having one handy in each of your vehicles as well as a few backups at base. Occasionally supplying an NPC with one (or more frequently if you get a lot of NPCs). Mounting a few on each of your vehicles. Carrying different ones for different situations.
Getting dangerous guns off the streets (literally) and into a relatively safe and secure armoury. Moral obligations and all that.
Or more commonly, because gaming has ingrained in you to hoard everything.
Tbh I collect most things because I don’t know what will be useful - I haven’t seen all the recipes and don’t know which will unlock using ceramic cups and the like. I guess I could partially solve this by having per-town screenshotted stashes so I could easily go back and gather what I need. But at that point… why not just haul it to base and have it 5 tiles away?
Guns and ammo are only a small part of storage, maybe 30L total. I haven’t yet raided any gun-heavy places. I also didn’t know that guns cannot ever break.
Well, technically they can break. If they accumulate a lot of fouling (usually from reloaded ammo) and you don’t clean it but keep shooting with it, it should take damage.
Also, if something gets too close and melee attacks you, you might block or counter attack with your gun, which can damage (and destroy) it too.
So it’s really rare, but if you don’t take care of your guns, don’t repair and clean them and abuse them a lot, they do break…
But I mean, I just hoard collect everything, so I do have also quite a bit of stuff in storage.
I mean a stationary base does provide everything you’ve just listed and more, with the only downside that it’s immobile.
I’m not sure how a vehicle can “provide you with food”, unless modded or if you used it to raid (which will provide less and less food, once stuff rots away and leaves behind only non-perishables). Farming on the other hand is infinite…
Also, (currently) NPC base camps can’t be made mobile, so if you want to play with them you have to settle somewhere, at least temporarily…
To each their own, but “can’t compete” is a bit strong worded and misleading in my opinion.
I suppose that one could still live an in-vehicle “nomadic” lifestyle with stationary farms. So, plant something and mark it, then return in 2-3 months/as needed to harvest. Could also combine this with general stashes of useless stuff, like excess clothing and 17" wheels.
True, but that would still mean that you’d have a “stationary base” you’d return to after a while…
If you want to keep moving in one direction or just freely travel around, this will not work.
Well no, you could also decide not to return (hence the “as needed”). You just know its there and how much, if required.
I’ve also been thinking of making an excess loot stash someplace else, as I have enough items at base for the processing time to be noticeable.
Oh, I know. A 5times2+ tiles towed vehicle full of cargo spaces. Then just leave it parked by the side of the road and tow it in as needed.
I just wish we could install “brakes by wire” to avoid getting rear-ended by the towed vehicle when decelerating.
I’ve dropped Elefant gun somewhere… 
I dragged a squad of MiGos through town and then set up in the megastore
Lots of shelves full of stuff, Big garage, glass roof in places so solar works indoors, large parking lot.
Its my second base, I started in the Prison and that seemed very secure once it was cleared. Even has room for a farm behind the walls, I just cant get a tractor in… yet
Of course once you have a good base, you spend nearly all your time away from it.